Mutations at Y-STR loci: implications for paternity testing and forensic analysis

Knowledge about mutation rates and the mutational process of Y-chromosomal short-tandem-repeat (STR) or microsatellite loci used in paternity testing and forensic analysis is crucial for the correct interpretation of resulting genetic profiles. Therefore, we recently analysed a total of 4999 male germline transmissions from father/son pairs of confirmed paternity (probability > or = 99.9%) at 15 Y-STR loci which are commonly applied to forensics. We identified 14 mutations. Locus specific mutation rate estimates varied between 0 and 8.58 x 10(-3), and the overall average mutation rate estimate was 2.80 x 10(-3) (95% CIL 1.72 x 10(-3)-4.27 x 10(-3)). In two confirmed father/son pairs mutation at two Y-STRs were observed. The probability of two mutations occurring within the same single germline transmission was estimated to be statistically not unexpected. Additional alleles caused by insertion polymorphisms have been found at a number of Y-STRs and a frequency of 0.12% was estimated for DYS19. The observed mutational features for Y-STRs have important consequences for forensic applications such as the definition of criteria for exclusions in paternity testing and the interpretation of genetic profiles in stain analysis. In order to further enrich our knowledge of Y-STR mutations we suggest the establishment of a Y-STR mutation database and ask the forensic community for data contribution.

An extensive analysis of Y-chromosomal microsatellite haplotypes in globally dispersed human populations

The genetic variance at seven Y-chromosomal microsatellite loci (or short tandem repeats [STRs]) was studied among 986 male individuals from 20 globally dispersed human populations. A total of 598 different haplotypes were observed, of which 437 (73.1%) were each found in a single male only. Population-specific haplotype-diversity values were.86-.99. Analyses of haplotype diversity and population-specific haplotypes revealed marked population-structure differences between more-isolated indigenous populations (e.g., Central African Pygmies or Greenland Inuit) and more-admixed populations (e.g., Europeans or Surinamese). Furthermore, male individuals from isolated indigenous populations shared haplotypes mainly with male individuals from their own population. By analysis of molecular variance, we found that 76.8% of the total genetic variance present among these male individuals could be attributed to genetic differences between male individuals who were members of the same population. Haplotype sharing between populations, phi(ST) statistics, and phylogenetic analysis identified close genetic affinities among European populations and among New Guinean populations. Our data illustrate that Y-chromosomal STR haplotypes are an ideal tool for the study of the genetic affinities between groups of male subjects and for detection of population structure.

Independent histories of human Y chromosomes from Melanesia and Australia

To investigate the origins and relationships of Australian and Melanesian populations, 611 males from 18 populations from Australia, Melanesia, and eastern/southeastern Asia were typed for eight single-nucleotide polymorphism (SNP) loci and seven short tandem-repeat loci on the Y chromosome. A unique haplotype, DYS390.1del/RPS4Y711T, was found at a frequency of 53%-69% in Australian populations, whereas the major haplotypes found in Melanesian populations (M4G/M5T/M9G and DYS390.3del/RPS4Y711T) are absent from the Australian populations. The Y-chromosome data thus indicate independent histories for Australians and Melanesians, a finding that is in agreement with evidence from mtDNA but that contradicts some analyses of autosomal loci, which show a close relationship between Australian and Melanesian (specifically, highland Papua New Guinean) populations. Since the Australian and New Guinean landmasses were connected when first colonized by humans > or =50,000 years ago but separated some 8,000 years ago, a possible way to reconcile all the genetic data is to infer that the Y-chromosome and mtDNA results reflect the past 8,000 years of independent history for Australia and New Guinea, whereas the autosomal loci reflect the long preceding period of common origin and shared history. Two Y-chromosome haplotypes (M119C/M9G and M122C/M9G) that originated in eastern/southeastern Asia are present in coastal and island Melanesia but are rare or absent in both Australia and highland Papua New Guinea. This distribution, along with demographic analyses indicating that population expansions for both haplotypes began approximately 4,000-6,000 years ago, suggests that these haplotypes were brought to Melanesia by the Austronesian expansion. Most of the populations in this study were previously typed for mtDNA SNPs; population differentiation is greater for the Y chromosome than for mtDNA and is significantly correlated with geographic distance, a finding in agreement with results of similar analyses of European populations.

Diversity and heterogeneity in mitochondrial DNA of North American populations

Variation in the mitochondrial DNA (mtDNA) control region as detected by sequence-specific oligonucleotide (SSO) probes is described for 2282 individuals from African-American, European-American, and Hispanic subpopulations from five broadly defined regions of North America (Northeast, Southeast, Central, Northwest, Southwest). Population diversity estimates were uniformly high for all subpopulations and for each major ethnic group. Only the Pennsylvania Hispanic group was remarkable with respect to its mitochondrial DNA types, having both six low frequency population specific types (ranging from 1.2-8.6%) and three high frequency shared types (10-20% each). There was no statistically significant subpopulation heterogeneity present within any of the three major groups at either the subpopulation level or the regional level (p > 0.01). However, statistically significant heterogeneity was measured when comparing the three major groups to each other, with the variance component attributable to this large division accounting for 18.60% of the total variance (p < 0.001). Overall mtDNA is a satisfactory forensic typing locus within broadly defined African-American, European-American, and Hispanic groups from North America, based on the high diversity estimates and absence of heterogeneity, as characterized by SSO typing.

Peripheral sympathetic function as a predictor of complex regional pain syndrome type I (CRPS I) in patients with radial fracture

Complex regional pain syndrome type I (CRPS I) is a frequent complication after injuries of the upper limbs. The pathophysiology of this disease remains unclear, although disturbances of the sympathetic nervous system have been detected in several clinical studies, and sympathetic blocks resolve the symptoms in many of the cases. To investigate the meaning of sympathetic dysfunction at the beginning of the disease, 27 patients with distal radial fracture were examined prospectively during the course of the disease with regard to their clinical symptoms and their peripheral sympathetic nervous function. Sympathetic nervous function was examined by testing the vasoconstrictor response to sympathetic stimuli--recorded with laser Doppler fluxmetry--of the fingertips of both hands. Four patients developed CRPS I during the 12-week observation time and two patients presented an incomplete clinical CRPS I picture ('borderline patients'). The complaints of all patients (normal fracture patients, CRPS I patients, borderline patients) were similar during the first week after trauma with focus on pain, motoric disturbances and autonomic symptoms. After 1 or 2 weeks, a larger clinical difference developed between normal fracture patients and CRPS I or 'borderline patients'. In CRPS I patients and 'borderline patients', the sympathetic vasoconstrictor response was diminished or absent from the first posttraumatic day throughout the observation time, whereas the normal fracture patients revealed slightly impaired sympathetic nervous function on the first posttraumatic day and normal results during the rest of the observation time. With regard to the unaffected contralateral hand, CRPS I patients also showed impaired sympathetic nervous function. The results of the present study suggest that the disturbances in the sympathetic nervous system in CRPS I patients are systemic and not limited to the affected limb. Their occurrence before the clinical breakout of the disease may serve as a marker that might be useful for early therapy and lead to further understanding of the pathophysiology of CRPS I.

Blaschkolinear skin pigmentary variation due to trisomy 7 mosaicism

Mosaic trisomy 7 is a rare condition that can be seen in individuals with Blaschkolinear skin pigmentary variation, somatic asymmetry, and variable other clinical anomalies. In any patient presenting with Blaschkolinear skin pigmentary variation, varying degrees of asymmetrical growth disturbance, developmental delay, and a normal lymphocytic karyotype, chromosomal mosaicism may be present. To rule out tissue-specific or occult chromosomal mosaicism, it is recommended to culture and karyotype skin fibroblasts, since lymphocyte cell lines may not demonstrate the abnormal cell line. Early diagnosis is of paramount importance, since early physical, occupational, and speech/language therapy can greatly improve the developmental outcome of these patients. We report on a fourth patient with trisomy 7 mosaicism in whom early diagnosis and developmental therapy contributed to an improved developmental outcome when compared with patients in previous reports. Early intervention can greatly benefit patients with this diagnosis, especially in minimizing the aggressive behavior associated with communication difficulties. Our patient has milder manifestations than the previously reported patients with no seizure activity or asymmetry and fewer cells with trisomy 7.

Melanesian origin of Polynesian Y chromosomes

BACKGROUND

Two competing hypotheses for the origins of Polynesians are the 'express-train' model, which supposes a recent and rapid expansion of Polynesian ancestors from Asia/Taiwan via coastal and island Melanesia, and the 'entangled-bank' model, which supposes a long history of cultural and genetic interactions among Southeast Asians, Melanesians and Polynesians. Most genetic data, especially analyses of mitochondrial DNA (mtDNA) variation, support the express-train model, as does linguistic and archaeological evidence. Here, we used Y-chromosome polymorphisms to investigate the origins of Polynesians.

RESULTS

We analysed eight single nucleotide polymorphisms (SNPs) and seven short tandem repeat (STR) loci on the Y chromosome in 28 Cook Islanders from Polynesia and 583 males from 17 Melanesian, Asian and Australian populations. We found that all Polynesians belong to just three Y-chromosome haplotypes, as defined by unique event polymorphisms. The major Y haplotype in Polynesians (82% frequency) was restricted to Melanesia and eastern Indonesia and most probably arose in Melanesia. Coalescence analysis of associated Y-STR haplotypes showed evidence of a population expansion in Polynesians, beginning about 2,200 years ago. The other two Polynesian Y haplotypes were widespread in Asia but were also found in Melanesia.

CONCLUSIONS

All Polynesian Y chromosomes can be traced back to Melanesia, although some of these Y-chromosome types originated in Asia. Together with other genetic and cultural evidence, we propose a new model of Polynesian origins that we call the 'slow-boat' model: Polynesian ancestors did originate from Asia/Taiwan but did not move rapidly through Melanesia; rather, they interacted with and mixed extensively with Melanesians, leaving behind their genes and incorporating many Melanesian genes before colonising the Pacific.

A new method for the evaluation of matches in non-recombining genomes: application to Y-chromosomal short tandem repeat (STR) haplotypes in European males

A 9-locus microsatellite framework (minimal haplotype), previously developed for forensic purposes so as to facilitate stain analysis, personal identification and kinship testing, has been adopted for the establishment of a large reference database of male European Y-chromosomal haplotypes. The extent of population stratification pertaining to this database, an issue crucial for its practical forensic application, was assessed through analysis of molecular variance (AMOVA) of the 20 regional samples included. Despite the notion of some significant haplotype frequency differences, which were found to correlate with known demographic and historic features of Europeans, AMOVA generally revealed a high level of genetic homogeneity among the populations analyzed. Owing to their high diversity, however, accurate frequency estimation is difficult for Y-STR haplotypes when realistic (i.e. moderately sized) datasets are being used. As expected, strong pair-wise and higher order allelic associations were found to exist between all markers studied, implying that haplotype frequencies cannot be estimated as products of allele frequencies. A new extrapolation method was therefore developed which treats haplotype frequencies as random variables and generates estimates of the underlying distribution functions on the basis of closely related haplotypes. This approach, termed frequency 'surveying', is based upon standard population genetics theory and can in principle be applied to any combination of markers located on the Y-chromosome or in the mitochondrial genome. Application of the method to the quality assured reference Y-STR haplotype database described herein will prove very useful for the evaluation of positive trace-donor matches in forensic casework.

Identification of the human Y-chromosomal microsatellite locus DYS19 from degraded DNA

STR DYS19 seems to be one of the most useful markers for population genetic, evolutionary, and forensic applications. However, the authors have noticed that the amplification of the DYS19 polymorphism fails when highly degraded DNA is used as a template. The authors designed a new pair of primers that reduce the DYS19 fragment sizes compared with those of the known protocol. Using these primers, an improved success rate can be achieved, particularly when putrefied samples are under investigation.

Paternity assessment in rhesus macaques (Macaca mulatta): multilocus DNA fingerprinting and PCR marker typing

Establishing kinship relations in primates using modern molecular genetic techniques has enhanced the ability to scrutinize a number of fundamental biological issues. We screened 51 human short tandem repeats (STRs) for cross-species PCR amplification in rhesus macaques (Macaca mulatta) and identified 11 polymorphic loci with heterozygosity rates of at least 0.6. These markers were used for paternity testing in three social groups (M, R, and S) of rhesus macaques from Cayo Santiago, Puerto Rico. Several consecutive birth cohorts were analyzed in which approximately 200 males were tested for paternity against more than 100 mother/ infant pairs. Despite a combined exclusion rate of more than 99.9% in all three groups, some cases could not be solved unequivocally with the STR markers and additional testing of the MHC-associated DQB1 polymorphism. A final decision became possible through multilocus DNA fingerprinting with one or more of the oligonucleotide probes (GATA)4, (CA)8, and (CAC)5. Paternity assessment by multilocus DNA analysis with probe (CAC)5 alone was found to have limitations in rhesus macaques as regards the number of potential sires which might be involved in a given case. Multilocus DNA fingerprinting requires large amounts of DNA, and the ensuing autoradiographic patterns present difficulties in comparisons across gels and even within the same gel across remote lanes. Computer-assisted image analysis was incapable of eliminating this problem. Therefore, a dual approach to DNA typing has been adopted, using STR markers to reduce the number of potential sires to a level where all remaining candidates can be tested by multilocus DNA fingerprinting on a single gel, preferably in lanes adjacent to the mother/infant pair.

Primary cutaneous cryptococcosis of the nose in an immunocompetent woman

Cutaneous manifestations of Cryptococcus neoformans in immunocompromised persons have been well documented. We report a case of localized skin involvement after an abrasion in a healthy host. It presented as chronic ulcerative nodules that resolved after fluconazole therapy.

Characteristics and frequency of germline mutations at microsatellite loci from the human Y chromosome, as revealed by direct observation in father/son pairs

A number of applications of analysis of human Y-chromosome microsatellite loci to human evolution and forensic science require reliable estimates of the mutation rate and knowledge of the mutational mechanism. We therefore screened a total of 4,999 meioses from father/son pairs with confirmed paternity (probability >/=99. 9%) at 15 Y-chromosomal microsatellite loci and identified 14 mutations. The locus-specific mutation-rate estimates were 0-8. 58x10-3, and the average mutation rate estimates were 3.17x10-3 (95% confidence interval [CI] 1.89-4.94x10-3) across 8 tetranucleotide microsatellites and 2.80x10-3 (95% CI 1.72-4.27x10-3) across all 15 Y-chromosomal microsatellites studied. Our data show a mutational bias toward length increase, on the basis of observation of more repeat gains than losses (10:4). The data are in almost complete agreement with the stepwise-mutation model, with 13 single-repeat changes and 1 double-repeat change. Sequence analysis revealed that all mutations occurred in uninterrupted homogenous arrays of >/=11 repeats. We conclude that mutation rates and characteristics of human Y-chromosomal microsatellites are consistent with those of autosomal microsatellites. This indicates that the general mutational mechanism of microsatellites is independent of recombination.

A polymorphic L1 retroposon insertion in the centromere of the human Y chromosome

We have identified a novel polymorphic L1 retroposon insertion, designated LY1, in the centromeric alphoid array of the human Y chromosome. The element belongs to the transpositionally active Ta subset and its presence is compatible with normal centromere function. It was found at highest frequency in China, where it accounts for 23% of the Han sample, and was present at low frequencies in the surrounding areas, but was not found at all outside Asia. Chromosomes carrying LY1 show considerable microsatellite diversity, suggesting an ancient origin for the lineage at approximately 10 000 years ago (with wide confidence limits), but only limited subsequent migration.

Towards understanding the origin and dispersal of Austronesians in the Solomon Sea: HLA class II polymorphism in eight distinct populations of Asia-Oceania

HLA class II nucleotide sequence polymorphisms were examined in eight ethnic groups of Asia-Oceania using DNA typing methods. Allele frequencies and characteristic DR/DQ haplotypes were determined and compared with those of other populations of Asia-Oceania. Genetic distances were measured to show the genetic relationship within the studied populations as well as between the studied populations and previously published populations. Phylogenetic trees were constructed based on HLA allele frequencies using the neighbour-joining method. The populations, mainly Trobriand Islanders, Roro, Tolai, Western Samoans and Taiwanese Aborigines, are characterized by a reduced diversity at the HLA loci examined, especially for DPB1. The high frequency of the 'Asian'-specific DPB1*0501 allele in Trobrianders and Roro, but also in Western Samoans and Taiwanese Aborigines, was the most striking result. The prevalence of DPB1*0501 and the short genetic distance from Trobriander and Roro to Taiwanese Aborigines provide evidence that the origin of the Austronesian odyssey is south-east Asia, and Taiwan could be an important part of it. The relatedness of Trobrianders to the Polynesian population from Western Samoa indicates a probable recent common ancestor. The observed lack of diversity may reflect bottleneck(s) and/or limited diversity of the founding population. Analysis of HLA class I antigens, together with mt-DNA and Y-chromosomal studies, will give us further information about the settlement of the Trobriand and other islands during the colonization of the Pacific.

Improving the stereoselectivity of bakers' yeast reductions by genetic engineering

[formula: see text] The stereoselectivities of bakers' yeast catalyzed reductions of beta-keto esters can be manipulated by genetic design. Strains in which two major beta-keto ester reductases are either knocked out or overexpressed have been constructed. The former approach results in whole cell biocatalysts with reversed stereoselectivity from unmodified bakers' yeast while the latter shows useful improvements in stereoselectivity. These results indicate that the "designer yeast" approach can provide useful biocatalysts for these transformations.

Molecular genetic evidence for the human settlement of the Pacific: analysis of mitochondrial DNA, Y chromosome and HLA markers

Present-day Pacific islanders are thought to be the descendants of Neolithic agriculturalists who expanded from island South-east Asia several thousand years ago. They speak languages belonging to the Austronesian language family, spoken today in an area spanning half of the circumference of the world, from Madagascar to Easter Island, and from Taiwan to New Zealand. To investigate the genetic affinities of the Austronesian-speaking peoples, we analysed mitochondrial DNA, HLA and Y-chromosome polymorphisms in individuals from eight geographical locations in Asia and the Pacific (China, Taiwan, Java, New Guinea highlands, New Guinea coast, Trobriand Islands, New Britain and Western Samoa). Our results show that the demographic expansion of the Austronesians has left a genetic footprint. However, there is no simple correlation between languages and genes in the Pacific.

Phylogenetic resolution of complex mutational features at Y-STR DYS390 in aboriginal Australians and Papuans

Y-chromosomal short tandem repeats (STRs) are used for the study of male aspects of human evolution as well as for forensic applications and paternity testing. Both applications require an understanding of the underlying mutational mechanisms that create variability. We describe complex mutations at the substructured DYS390 STR locus in 97 natives of the New Guinea/Australian region. Sequencing of short alleles in these populations indicates multirepeat deletions. All samples are further characterized using the five additional Y-STR loci DYS19, DXYS156-Y, DYS391, DYS392, and DYS393. Phylogenetic analysis of the resulting haplotypes yields ethnically specific clusters predating the settlement of Australia and Papua New Guinea (although archaic Homo sapiens or Homo erectus lineages are absent). The phylogeny confirms that DYS390 violates the stepwise mutation model and demonstrates that the DYS390 locus mutates relatively rapidly and retains its variability after structural change.

Subchronic inhalation toxicity study of caprolactam (with a 4-week recovery) in the rat via whole-body exposures

This study was designed to assess the potential subchronic inhalation toxicity of caprolactam when administered as a 3-micron aerosol from an aqueous solution to Sprague-Dawley CD rats (10/sex/group) via whole-body exposure. The study was enhanced with the inclusion of motor activity measurements and a functional observational battery to assess the neurotoxic potential of caprolactam. The rats were exposed at least 65 times over a 13-week period for 6 h per day, 5 days per week, to target concentrations (3 microns, mass median aerodynamic diameter) of 0, 25, 75, and 250 milligrams per cubic meter (mg/m3). An additional 10 animals/sex/group were similarly exposed and then held for a 4-week recovery period. Exposure levels were determined gravimetrically six times daily; one daily sample was analyzed by high-pressure liquid chromatography. No deaths were observed in the study during the exposure or recovery periods. Treatment-related responses such as labored breathing and nasal discharge were seen during many of the exposures. Similar responses as well as moist rales were seen during the nonexposure periods during the 13 weeks of exposure. However, these responses abated during the 4-week recovery period. There were no clearly treatment-related responses observed with ophthalmoscopic examinations, body weight measurements, food consumption measurements, neurobehavioral evaluations, clinical pathology evaluations, organ weight measurements, or macroscopic pathology examinations. Microscopic findings that were considered related to exposure to the test material were seen in the nasoturbinal tissues (hypertrophy/hyperplasia of goblet cells in the respiratory mucosa and intracytoplasmic eosinophilic material in epithelial cells of the olfactory mucosa) of the two higher-exposure group animals and in the laryngeal tissues (squamous/squamoid metaplasia/hyperplasia of the pseudostratified columnar epithelium covering the ventral seromucous gland) of all three exposure group animals. These changes were considered to be adaptive responses to an irritant (caprolactam). The keratinization of the metaplastic epithelium in the larynx was considered to be an adverse effect. By the end of the 4-week recovery period, there was complete regression of the keratinization in the larynx, but recovery of the adaptive nasoturbinal effects had not completely resolved. In conclusion, the whole-body exposure of Sprague-Dawley rats to caprolactam as a respirable aerosol for 6 h/day, 5 days/week, for 13 weeks at gravimetrically determined levels of 24, 70, and 243 mg/m3 resulted in respiratory tract effects (laryngeal) at the highest exposure level with complete recovery within 4 weeks postexposure. The results indicate that the no-observed-adverse-effect level for caprolactam is 70 mg/m3, based on upper respiratory effects, with 243 mg/m3 representing a no-observed-effect level for systemic toxicity, neurotoxicity, and lower respiratory tract effects.

Subchronic toxicity studies of 3-methyl-1-butanol and 2-methyl-1-propanol in rats

1. 90-day subchronic toxicity studies with 3-methyl-1-butanol (MEB) and 2-methyl-1-propanol (MEP) were performed on rats to evaluate the toxicological profile of the compounds under conditions of drinking water studies, to identify the potential target organs, and to determine no-observable-adverse-effect-levels (NOAELs) respective of the substances. The test substances were administered to groups of 10 male and 10 female Wistar rats in drinking water at concentrations of 0, 1000 p.p.m. (about 80 mg/kg/d), 4000 p.p.m. (about 340 mg/kg/d) and 16,000 p.p.m. (about 1250 and 1450 mg/kg/d of MEB and MEP respectively). 2. 16,000 p.p.m. was found to be the maximal concentration for both alcohols applicable to rats in drinking water. Higher concentrations had an influence on palatability and could thus not be tested in drinking water studies. 3. At 16,000 p.p.m. MEB a marginal increase in the red blood cell count as well as a slight decrease in the mean corpuscular volume and the mean corpuscular hemoglobin content was observed in males only. These changes are considered to be treatment-related, although the toxicological significance of these findings is unclear. No other substance-related effects were found on body weight (b.w.), mortality, various parameters of clinical chemistry, organ weights, gross pathology and histopathology. 4000 p.p.m. MEB did not cause any substance-induced changes. Therefore, the NOAEL of MEB was defined as 4000 p.p.m. for male and 16,000 p.p.m. for female rats under conditions of oral application via drinking water. 4. MEP concentrations up to and including 16,000 p.p.m. did not induce any signs of toxicity and were therefore defined as the NOAEL respective of this substance for rats under conditions of drinking water application.

Applications of microsatellite-based Y chromosome haplotyping

Y-chromosomal microsatellites have been investigated for the purposes of application to male identification, population genetics and population history. With nine markers, every male in a German population sample (n = 70) could be identified by an individual-specific Y microsatellite haplotype. The analysis of 474 unrelated males of nine human populations with seven markers revealed 301 different Y haplotypes. The analysis of molecular variance (AMOVA) approach was used to detect male population characteristics of Y microsatellite haplotypes. With pairwise comparisons of inter-population variance, most of the populations could be distinguished significantly. Sixty individuals from different male populations in Asia and Northern Europe carrying a novel Y-chromosomal T-->C transition show reduced microsatellite variability together with haplotype similarities. Microsatellite data suggest that the mutation occurred recently in Asia, supporting the hypothesis of Asian ancestry of some northern European populations.

Genetic relationships of Asians and Northern Europeans, revealed by Y-chromosomal DNA analysis

We have identified a new T-->C transition on the human Y chromosome. C-allele chromosomes have been found only in a subset of the populations from Asia and northern Europe and reach their highest frequencies in Yakut, Buryats, and Finns. Examination of the microsatellite haplotypes of the C-allele chromosomes suggests that the mutation occurred recently in Asia. The Y chromosome thus provides both information about population relationships in Asia and evidence for a substantial paternal genetic contribution of Asians to northern European populations such as the Finns.

The dependence of osteoblastic response on variations in the chemical composition and physical properties of hydroxyapatite

Two synthetic hydroxyapatite powders (A and B), supplied by different manufacturers, were physically and chemically characterized before being die pressed and sintered at 1250 degrees C. The powders were characterized using X-ray diffraction (XRD), infrared spectroscopy (IRS), X-ray fluorescence, surface area analysis (BET), particle size analysis and scanning electron microscopy (SEM). The materials were then pressed and sintered to produce hydroxyapatite discs of similar densities and grain sizes for in vitro evaluation. The ceramics were seeded with osteoblastic cells and after 15 days in culture the cell morphology was assessed using scanning electron microscopy (SEM), the ultrastructure of the cells was studied using transmission electron microscopy (TEM) with EDAX, and the rate of cell growth was assessed using biochemical techniques. The results clearly showed that the rate of cell proliferation but not the rate of alkaline phosphatase production, was highly dependent on the composition of the hydroxyapatite powders that were used to make the ceramic discs. The ultrastructural studies confirmed the relative viabilities of the cells and the nature of the ceramic interface indicating visually the marked differences in the performance of the two materials.